B2H6 oxidation

Whatley and Pease re-examined this system a few years later. Their lower ignition limits agreed with those of Price, but their upper pressure limits were larger at any temperature. The mixtures exploded with an induction period, which suggested to Whatley and Pease that a slowly formed pyrolysis product (perhaps pentaborane) was the sensitizing agent. 

Roth and Bauer found a third limit which depended on vessel diameter. Their second limit was not dependent on the vessel diameter, but their results differed from the earlier values . However, as did Whatley and Pease, they obtained larger values than Price for the pressure at the second explosion limit. Roth and Bauer wrote a simplified mechanism 

In another paper, they Reported the effect of N2, He, Ar, and H2 on the second explosion limit. The results indicated third-order chain-terminating steps. Later results from the same laboratory showed that some H2O, HBO2 and B(OH)3 

The above mechanism must be considered speculative at this time. One shortcoming is its failure to explain all the products. Furthermore, it is difficult to understand the need for a chaperone gas in reaction (4). Also as pointed out by Gob-bett and Linnett , there is no direct evidence for oxygen atoms in the system. 

Parker and Wolfhard °° studied the combustion of B2Hg-air mixtures and measured the limits of flame propagation, burning velocity, and rate of pressure rise during explosion in a closed vessel. For this system, Breisacher et monitored the H2 produced. They proposed a mechanism in which, by analogy to CH3 oxidation, BH3 and O2 react to form BH3OO which subsequently decomposes. 

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Reagents i, H20-dioxan-Na2C03 ii, dehydration iii, B2H6-oxidation iv, Jones oxidation v, LiNPr -THF vi, Me3SiCl vii, 03-Me0H-CH2Cl2 viii, NaBH4 ix, aq. HCl. 

With this as introduction, let us now look at the individual steps in more detail for the case of hydroboration-oxidation of 1-decene. A boron hydride that is often used is dibomne (B2H6). Diborane adds to 1-decene to give tridecylborane according to the balanced equation ... 

The first of the nudeophilic ring-opening reactions of vinylaziridines discussed in this section is diborane reduction, developed by Laurent and coworkers in 1976 (Scheme 2.24). Treatment of N-unsubstituted vinylaziridines 89 with B2H6 gives allyl amines 92 by SN2 reduction via cyclic intermediates 90 [40]. In contrast, treatment with 9-BBN gives 2-(hydroxyethyl)aziridines 93 after oxidative workup (Scheme 2.25) [41]. 

Anri-Markownikov hydration of alkenes may be effected indirectly by addition of B2H6 (hydroboratiori), followed by oxidation of the... 

Hydroboration, the addition of a boron-hydrogen bond across an unsaturated moiety, was first discovered by H. C. Brown in 1956. Usually, the reaction does not require a catalyst, and the borane reagent, most commonly diborane (B2H6) or a borane adduct (BH3-THF), reacts rapidly at room temperature to afford, after oxidation, the /AMarkovnikov alkene hydration product. However, when the boron of the hydroborating agent is bonded to heteroatoms which lower the electron deficiency, as is the case in catecholborane (1,3,2-benzodioxaborole) 1 (Scheme 1), elevated temperatures are needed for hydroboration to occur.4 5... 

This enantioselective reduction can be used for synthesis of chiral 1-substituted oxiranes.1 2 3 Thus reduction of 2-chloroacetophenone with B2H6 catalyzed by 1 (1 mole %) results in (S)-( + )-(chloromethyl)benzenemethanol, which in the presence of base converts to (S)-( - )-phenyloxirane (styrene oxide). 

LiBH4 + 2HC1 2LiCl + B2H6 + 2H2 Reactions with oxidizing agents are violent. 

H.8 The reaction of boron trifluoride, BF3(g), with sodium borohydride, NaBH4(s), leads to the formation of sodium tetrafluoroborate, NaBF4(s), and diborane gas, B2H6(g). The diborane reacts with the oxygen in air, forming boron oxide, B203(s), and water. Write the two balanced equations leading to the formation of boron oxide. 

This basic system was designed to deposit Si02 from the SiH4 + 02 reaction at about 400°C and atmospheric pressure. It can also deposit doped oxides by introducing PH3 for phosphorus doping or B2H6 for boron doping. In order to protect personnel from these toxic dopants, the reactor is housed in a vented enclosure. 

Such an anti-Markovnikov hydration was impossible until H. C. Brown, of Purdue University, discovered that diborane (B2H6) adds to alkenes with anti-Markovnikov orientation to form alkylboranes, which can be oxidized to give anti-Markovnikov alcohols. This discovery led to the development of a large field of borane chemistry, for which Brown received the Nobel Prize in Chemistry in 1979. 

Reagents i, NaOEt ii, CH2N2 iii, Jones oxidation iv, acetalization v, B2H6 vi, H202-Na0H ... 

It is notable that BH4 also undergoes one-electron oxidation to produce H2 and BH3 (B2H6). The BH3 thus formed can be utilized for in situ hydroboration of olefins [105,106]. 

Reaction of H2 with B2CU in the gas phase forms B(III) productsS BCI3 and B2H6. With a less reactive diboron compound, an oxidative-addition or reductive-elimination sequence is observed ... 

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